1. Field of the Invention
This invention relates to subterranean containment of hazardous waste material and more particularly to the storage of both low-level and high-level radioactive waste material in sealed containers that are encapsulated in cement modules stored in an underground mine that maintains stabilized positioning of the containers while providing drainage, ventilation, and access to the containers for periodic inspection.
2. Description of the Prior Art
The containment and disposal of hazardous waste material, including toxic substances and radioactive waste, is regulated by the United States Environmental Protection Agency and the Nuclear Regulatory Commission. In general, the regulations require that the hazardous materials be handled and contained in a manner that does not contaminate the environment or threaten the public health.
It is well known to store radioactive and toxic wastes in steel barrels or drums which then are stored for long term containment requiring that precautions be taken to prevent release of the hazardous waste into the environment. Consequentially, the barrels or drums must be stored in a structure that assures that the hazardous waste will be safely and permanently contained. Consequentially, provisions must be made at the storage site to prevent leaching of the hazardous waste into the soil of the underground formation and therefrom into the ground water supply. The containers must be stabilized to resist damage resulting from subsidence, earthquake, and other seismic activity. In the case of hazardous waste that generates heat, the storage site must be ventilated to prevent thermal deterioration of the containment site.
An example of containment of radioactive waste in conventional 55 gallon steel drums is disclosed in U.S. Pat. No. 3,935,467. A repository for the drums includes an elongated tube of bituminous fibre material closed at its end by treated plywood caps. A plurality of the steel drums containing the waste material is positioned in axial alignment and in spaced relation within the tube. The drums are encapsulated within the tube and spaced from one another by polyurethane foam. The foam is injected in place and completely fills the inner cavity of the tube around each drum so that the drums are separated from one another. The foam stabilizes the drums inside the tube to prevent physical damage to the drums. The foam also serves to prevent hazardous materials, such as chemicals, from seeping out of the drums. The foam prevents ground water and water vapor from coming in contact with the metal containers. A plurality of tubes containing the encapsulated metal drums can be stacked above or below ground for permanent storage.
U.S. Pat. No. 3,983,050 discloses a method for storing high-level radioactive wastes in metal canisters lined with powdered cement which mixes with water leaking into the canister to form a cement patch. The containment of hazardous waste material in cylindrical drums is also disclosed in U.S. Pat. No. 4,863,638 in which a plurality of stacked drums are banded together so that the drums are fixedly secured with respect to one another. The banded drums are then encapsulated within a plastic casing formed by a molding operation. A number of legs are attached to the bottom of the casing for positioning the casing on any type of floor area, such as an ocean floor area or landfill area.
A further example of underground storage of drums containing radioactive waste is disclosed in U.S. Pat. No. 3,255,896. The drums are stored in an underground channel structure having access openings for inspecting the containers. The containers are provided with rollers that permit the containers to be rolled into position in the channel structure.
In the dry storage of hazardous waste material, the material is contained within multiple barrier layers. The first barrier layer may include a tubular structure sealed within a concrete structure as disclosed in U.S. Pat. No. 4,834,916, or as an alternative a waste containing drum is encased within an inner lead containing shield which, in turn, is surrounded by an outer concrete receptacle as disclosed in U.S. Pat. No. 4,229,316. The receptacle is provided with tubes extending through concrete and lead enclosures for adding radioactive material into the inner container. The surrounding containers are also provided with passages for venting gases from the surrounding layers.
Another example of a multilevel above-ground repository for radioactive waste is disclosed in U.S. Pat. No. 4,842,774. The multilevel repository includes a number of containment areas arranged in a pyramidal configuration. Each containment area includes a floor and a roof formed of compacted clay to shed water away from the area. The containment areas are separated by shield walls made of either steel reinforced concrete or by a wall-shaped stack of castable concrete containers which also contain radioactive waste imbedded in concrete. Waste containers are then stacked within the areas between the shield walls.
A disposal site adaptable for aboveground and underground storage of hazardous and toxic wastes is disclosed in U.S. Pat. No. 4,844,840. The disposal site is formed over an impermeable bed which acts to collect the leachate and prevent its penetration into the ground water. The bed includes multiple layers of different types of materials, such as clay, sand, soil and gravel. The top layer is a graveled layer upon which waste canisters are stacked. The multiple layers of canisters are stacked in interlocking relation. Each canister is a reinforced concrete receptacle having a removable cover. Waste containing barrels and boxes are placed within each concrete receptacle, and the spaces between barrels within receptacles are filled with a curable fluid sealant, such as grout. The stacked canisters are sealed within a penetration barrier formed by layers of synthetic liner, clay, gravel, and soil.
U.S. Pat. No. 4,586,849 discloses a further example of an underground radioactive waste repository in which a horizontal shaft is bored into the side of a mountain. The shaft is located between two layers of rock which are substantially impervious to water. A number of side passages extend from the main shaft. The radioactive waste material is stored at the ends of the side passages in storage areas behind lead lined shielding. The waste material is contained in casings which are then stacked in the storage areas.
While it is well known to dispose of hazardous waste material by storage in containers encased in aboveground and underground repositories, a repository must be constructed exclusively as a disposal site. In underground mining operations the excavated areas are abandoned after the mine material is extracted. Therefore, there is need to utilize abandoned underground excavated areas as repositories for the storage and disposal of hazardous waste material.